getw(3C)

Name

fgetc, getc, getc_unlocked, getchar, getchar_unlocked, getw - get a byte from a stream

Synopsis

#include <stdio.h>
int fgetc(FILE *stream);

int getc(FILE *stream);

int getc_unlocked(FILE *stream);

int getchar(void);

int getchar_unlocked(void);

int getw(FILE *stream);

Description

The fgetc() function obtains the next byte (if present) as an unsigned char converted to an int, from the input stream pointed to by stream, and advances the associated file position indicator for the stream
(if defined).

For standard-conforming (see standards(5)) applications, if the end-of-file indicator for the stream is set, fgetc() returns EOF
whether or not a next byte is present.

The getc() function is functionally identical to fgetc(), except that it is implemented as a macro. It runs faster than fgetc(), but it takes up more space per invocation and its name cannot be passed as an argument to a function call.

The getchar() routine is equivalent to getc(stdin). It is implemented as a macro.

The getc_unlocked() and getchar_unlocked() routines are variants of getc() and getchar(), respectively, that do not lock the stream. It is the caller's responsibility to acquire the stream lock before calling these
routines and releasing the lock afterwards; see flockfile(3C) and stdio(3C). These routines are implemented as macros.

The getw() function reads the next word from the stream. The size of a word is the size of an int and may vary from environment to environment. The getw() function presumes no special alignment in the file.

The getw() function may mark the st_atime field of the file associated with stream for update. The st_atime field will be marked for update by the first successful execution of fgetc(), fgets(3C), fread(3C), getc
(), getchar(), gets(3C), fscanf(3C) or scanf(3C) using stream that returns data not supplied by a prior call to ungetc(3C).

Return Values

Upon successful completion, fgetc(), getc(), getc_unlocked(), getchar(), getchar_unlocked(), and getw() return the next byte from the input stream pointed to by stream.
If the stream is at end-of-file, the end-of-file indicator for the stream is set and these functions return EOF. For standard-conforming (see standards(5)
) applications, if the end-of-file indicator for the stream is set, these functions return EOF whether or not the stream is at end-of-file. If a read error occurs, the error indicator for the stream is set, EOF is returned, and errno
is set to indicate the error.

Errors

The fgetc(), getc(), getc_unlocked(), getchar(), getchar_unlocked(), and getw() functions will fail if data needs to be read and:

EAGAIN

The O_NONBLOCK flag is set for the file descriptor underlying stream and the process would be delayed in the fgetc() operation.

EBADF

The file descriptor underlying stream is not a valid file descriptor open for reading.

EINTR

The read operation was terminated due to the receipt of a signal, and no data was transferred.

EIO

A physical I/O error has occurred, or the process is in a background process group attempting to read from its controlling terminal, and either the process is ignoring or blocking the SIGTTIN signal or the process group is orphaned. This error may also be generated
for implementation-dependent reasons.

EOVERFLOW

The file is a regular file and an attempt was made to read at or beyond the offset maximum associated with the corresponding stream.

A request was made of a non-existent device, or the request was outside the capabilities of the device.

Usage

If the integer value returned by fgetc(), getc(), getc_unlocked(), getchar(), getchar_unlocked(), and getw() is stored into a variable of type char and then
compared against the integer constant EOF, the comparison may never succeed, because sign-extension of a variable of type char on widening to integer is implementation-dependent.

The ferror(3C) or feof(3C) functions
must be used to distinguish between an error condition and an end-of-file condition.

Functions exist for the getc(), getc_unlocked(), getchar(), and getchar_unlocked() macros. To get the function form, the macro name must be undefined (for example, #undef getc).

When the macro forms are used, getc() and getc_unlocked() evaluate the stream argument more than once. In particular, getc(*f++); does not work sensibly. The fgetc
() function should be used instead when evaluating the stream argument has side effects.

Because of possible differences in word length and byte ordering, files written using getw() are machine-dependent, and may not be read using getw() on a different processor.

The getw() function is inherently byte stream-oriented and is not tenable in the context of either multibyte character streams or wide-character streams. Application programmers are recommended to use one of the character-based input functions instead.